Telescopes and similar optical instruments may be supported by adjustable mounts, which are capable of adjusting the orientation of the optical instrument for viewing different objects. One popular optical instrument mount is the altitude-azimuthal mount, referred to hereinafter as the “alt-az mount”. FIG. 1A is an isometric view of a prior art alt-az mount 10. FIG. 1B is an isometric view of alt-az mount 10 in use to support telescope tube 20 as part of a prior art telescope system 15. FIGS. 1C and 1D are a pair of schematic side elevation views of mount 10 and telescope system 15 which are useful for explaining the functionality thereof.
Mount 10 includes a generally vertical extending arm 12A and a generally horizontally extending arm 12B. Horizontal arm 12B is coupled to a level surface 14 via an azimuthal pivot joint 16. In telescope system 15, level surface 14 is provided by a tripod 14A or similar leveling system. Tripod 14A ensures that level surface 14 (and consequently horizontal arm 12B) are generally horizontally oriented and vertical arm 12A is generally vertically oriented. When mount 10 is leveled in this manner, pivot joint 16 coupled between tripod 14A and horizontal arm 12B permits pivotal movement of mount 10 about a generally vertically oriented axis 16A known as an azimuthal axis 16A.
Mount 10 also comprises an instrument coupling mechanism 19 by which an optical instrument (e.g. a telescope) 20 is coupled to vertical arm 12A. Instrument coupling mechanism 19 can take a wide variety of forms, depending on the particulars of the mechanism used to couple optical instrument 20 to vertical arm 12A. By way of non-limiting example, instrument coupling mechanisms 19 can include screw-based connection mechanisms, tongue and groove-based connection mechanisms, deformable (e.g. snap together) connection mechanisms and/or the like. Despite a variety of connection mechanisms, instrument coupling mechanisms 19 of alt-az optical instrument mounts (e.g. mount 10) tend to comprise: one or more instrument-engaging components 17 which fixedly engage optical instrument 20; and a pivot joint 18 coupled between instrument-engaging component(s) 17 and an edge or surface of vertical arm 12A which permits pivotal movement of instrument-engaging component(s) 17 and optical instrument 20 about a generally horizontally oriented axis 18A known as an altitude axis 18A.
Alt-az mounts (e.g. mount 10) are popular for telescope systems because alt-az mounts can be made relatively robust to support large telescope tubes (e.g. Dobsonian telescope tubes) and alt-az mounts can be fabricated from relatively inexpensive components.
The orientation of telescope 20 about altitude axis 18A and azimuthal axis 16A correspond to a set of coordinates referred to as altitude-azimuthal coordinates or alt-az coordinates. Alt-az coordinates are typically expressed in degrees of altitude (Alt) and degrees of azimuth (Az). Alt represents the angular orientation of telescope 20 about altitude axis 18A relative to the horizon and is typically expressed in a range of −90° ≦Alt≦90°. The point at Alt=90°(i.e. directly overhead) is referred to as the zenith. Az represents the angular orientation of instrument 20 about azimuthal axis 16A and has a range of 0° ≦Az≦360°. Typically, Az is selected to represent the true (as opposed to magnetic) compass heading toward a point on the horizon and is measured eastwardly from North (i.e. North=0°; East=90°; South=180°; and) West=270°.
One characteristic of telescope systems employing alt-az mounts (like mount 10) is that every observer location on Earth has its own unique alt-az coordinate system. That is, the alt-az coordinates of particular objects (e.g. celestial objects) depend on the observer location. Accordingly, telescope users do not typically use alt-az coordinates to share information about the location of celestial objects.
Instead, telescope users typically describe the location of celestial objects in celestial coordinates. Celestial coordinates may also be referred to as “polar coordinates” or “equatorial coordinates” and are based on the notion of a celestial sphere centered at the Earth and having an undefined radius. Celestial coordinates describe the angular position of a celestial object on the celestial sphere in a manner that is independent of the observer location.
Celestial coordinates are expressed in degrees of declination (DEC) and hours of right ascension (RA). DEC represents a projection of the Earth's terrestrial latitude onto the celestial sphere. DEC has a range of −90°≦DEC≦90°, where 0° is the projection of the Earth's equator (referred to as the “celestial equator”) and ±90° are the projections of the axis about which the Earth rotates (referred to as the “celestial poles”). RA is defined by longitudinal lines (typically referred to as “hour circles”), which intersect the North and South celestial poles. Unlike the earth's lines of longitude, the hour circles of RA remain fixed on the celestial sphere.
RA is normally expressed in hours, minutes and seconds and has a range of 0 hours≦RA≦24 hours, where 1 hour=15°. RA=0 hours has been arbitrarily assigned to be the hour circle coinciding with the projection of the Earth's vernal (spring) equinox on the celestial sphere. RA increases in an eastward direction until it returns to 24 hours at the hour circle coinciding with the projection of the Earth's vernal equinox again.
The Earth is continually rotating about its axis. Consequently, even though celestial coordinates are capable of describing the position of a celestial object in a manner that is independent of the observer location, orientation information relating to the location of the observer on the surface of the earth is still required in order use the celestial coordinates of the object to capture the object in the field of view of a telescope. This orientation information may include a variety of parameters which effectively specify the instantaneous orientation of the observer location (which is moving as the earth rotates) with respect to the celestial coordinate system. Typically, this orientation information includes the latitude of the observer location and the instantaneous sidereal time at the observer location. However, other mathematically equivalent forms of orientation information may also be used for this purpose.
This orientation information, which specifies the instantaneous orientation of the observer location with respect to the celestial coordinate system may also be used to formulate a transformation between the celestial coordinate system and a local alt-az coordinate system at the observer location. Such a transformation may transform the coordinates of a celestial object from the celestial coordinate system to the local alt-az coordinate system and may thereby determine the instantaneous altitude and azimuthal angles (Alt, Az) to which telescope 20 must be oriented about respective axes 18A, 16A of alt-az mount 10 to capture the celestial object in the field of view of telescope 20.
Using this orientation information to compute transformations between celestial and alt-az coordinate systems can be complex and burdensome, particularly for amateur or mathematically unsophisticated telescope users. Consequently, telescope systems having alt-az mounts (like mount 10) have been devised which: allow a user to select a desired celestial object specified in celestial coordinates (or to otherwise input desired celestial coordinates); obtain (through user input or otherwise) suitable orientation information about the particular observation location of the telescope system; use the orientation information to transform the desired celestial coordinates into desired local alt-az coordinates; and automatically configure the alt-az mount (i.e. move telescope about the altitude and azimuthal axes) to orient the telescope toward the desired location alt-az coordinates. These telescope systems may be referred to “go-to” telescope systems, because they automatically compute alt-az coordinates and cause the telescope to “go to” alt-az coordinates corresponding to desired celestial objects/coordinates.
Go-to telescope systems typically incorporate a variety of suitable hardware and software for implementing the go to functionality. By way of non-limiting example, go-to telescope systems can comprise electronic hardware (e.g. user interface components, communications components and/or the like), motors and related motor control hardware (e.g. transmissions or other drive mechanisms for operative connecting motors to the altitude and azimuthal pivot joints, position sensors for the altitude and azimuthal pivot joints, amplifiers and driving circuitry for driving the motors and/or the like), suitably programmed processing hardware (e.g. processors configured to compute the transformations between celestial and alt-az coordinates and to otherwise control the functionality of the go-to system).
Celestial objects viewed through a telescope appear to move through the sky. This apparent movement of celestial objects is principally due to the rotation of the Earth about its axis. There are other factors (e.g. the motion of the Earth around the sun and the motion of an object itself), which cause the object to appear to move through the sky, but these factors are usually very small over the course of an observing session. Accordingly, after locating a desired celestial object, the orientation of a telescope must be continually adjusted in order to maintain the object in the telescope field of view. Continual adjustment of a telescope orientation to maintain a desired celestial object in the telescope field of view is referred to as “tracking” an object.
Tracking a celestial object as is moves through the sky can also be burdensome, particularly for amateur telescope users. Consequently, some go-to telescope systems having alt-az mounts (like mount 10) have been provided with additional control software which provides the ability to automatically track the movement of celestial objects. Such telescope systems may be referred to as “auto-tracking” telescope systems.
Referring again to FIGS. 1A-1D, a problem with prior art alt-az mount 10 is shown in FIG. 1D. For long optical instruments (e.g. telescopes 20), physical interaction between the body of telescope 20 and horizontal arm 12B limits the range of pivotal motion of telescope 20 about altitude axis 18A (oriented into and out of the page in the FIG. 1D view). The dotted outline of telescope 20 in FIG. 1D illustrates these limits, where the body of telescope 20 contacts horizontal arm 12B at location 22A when telescope 20 is pivoted around altitude axis 18A too far in one angular direction and at location 22B when telescope 20 is pivoted around altitude axis 18A too far in the opposing angular direction.
Without risking damage to telescope 20 or mount 10, the potential for contact between telescope 20 and horizontal arm 12B can limit the ability of using mount 10 to view objects that have alt coordinates above an upper limit (alt>altmax|altmax>0°) or below a lower limit (alt<−altmin|altmin>0°). These limits can be particularly problematic in the context of go to telescope systems and auto-tracking telescope systems, where a processor controls motors to automatically configure the orientation of telescope 20 and may not have knowledge of the size of telescope 20. If these limits are not set correctly to corresponding to the size of the current telescope 20 on mount 10, then the automatic control of the telescope orientation can cause damage to telescope 20.
There is a general desire to provide alt-az mounts for optical instruments which eliminate or ameliorate this constraint on the altitude adjustment range.
For some applications (e.g. capturing panoramic images where individual images are stitched together or using similar techniques), there is a desire to adjust the position of an optical instrument 20 relative to vertical arm 12A of alt-az mount 10, such that the optical axis 20A of instrument 20 is in the plane of (i.e. coplanar with) the plane of azimuthal axis 16A. This situation can be seen in FIG. 1C, where optical axis 20A of instrument 20 is oriented into and out of the plane of the FIG. 1C page. For particular applications, it might be desirable to adjust the position of optical instrument 20 relative to vertical arm 12A to the position 20′ indicated by dotted outline, such that its optical axis 20A′ is coplanar with azimuthal axis 16A for any orientation of optical instrument 20 about altitude axis 18A.
Adjustment of the position of optical instrument 20 relative to vertical arm 12A may be accomplished by adjusting the configuration of instrument coupling mechanism 19 and/or adjusting the position of optical instrument 20 relative to instrument coupling mechanism 19. It will be appreciated that the range of adjustability of the position of optical instrument 20 relative to vertical arm 12A is limited by the width of optical instrument 20—i.e. because of the interaction between instrument 20 and the edge or surface of vertical arm 12A, a wider instrument 20 will have a correspondingly lower range of adjustability relative to vertical arm 12A. Ultimately, for a given mount 10 and instrument coupling mechanism 19, some optical instruments 20 may be too wide to adjust to a position where their optical axes 20A are coplanar with azimuthal axis 16A.
There is a general desire to accommodate wide optical instruments on alt-az mounts while permitting the optical axes of the instruments to be coplanar with the azimuthal axis of the mount for any orientation of the instruments about the altitude axis and/or to otherwise maximize the adjustability of the position of optical instruments relative to the vertical arm of alt-az mounts.